The present invention relates to apparatus for blocking the movement and/or feeding of roving to the draw frame of a spinning device.
It is known to provide a slubbing or roving blocking device having a member which moves into a blocking position between the lower entry roll and the upper entry roll of a draw frame in the event of yarn breakage, and which lifts the upper feed roll from the lower feed roll, while holding the roving fast between itself and the upper roller (DE-PS No. 3 21 196 and DE-OS No. 20 48 579.
The part of the roving not held fast is moved further along the spinning path by the drawing pair of drawing rollers which continue to remain in an operating condition, so that a fiber tuft is formed in the area between the entry roller pair and the blocking point of the drawing roller pair. This fiber tuft, however, constitutes the initial section of the roving necessary to repiece the yarn, after removal of the blockage and restart of spinning. Fiber tufts may differ greatly in their length and cross section, with the result that variable prerequisites are created for the subsequent repiecing. Substantial differences also result from the roving material used, depending on whether it is a cotton or worsted yarn.
For example, cotton has a relatively short staple length, and therefore, the distances between the entry rollers and the succeeding drawing roller pairs (referred to as the forefield) is selected so that it is between one and a half and twice the mean staple length. The drawing roller pair is, as a rule, a twin belt unit running over a pair of solid rollers which act to twist the fibers into the thread. A cotton fiber tuft will finally stand free in the area of the forefield, and will approach the drawing rollers at variable distances, depending on the share of floating fibers still remaining in the blocked part of the roving, i.e. those fibers which are located neither in the blocking device nor in the nip formed by the drawing pair of belts. Part of the floating fibers are carried along after blockage is effected by the fibers already present in the twisting belts as well as those continuing to enter the latter.
A worsted yarn roving has, however, a share of fibers which are distinctly longer than the length of the normal forefield. It is for this reason that the roller pairs over which the twisting belts pass contain at least one roll having an annular channel by means of which the fibers running into the twin-belt unit may be pulled tight but not torn. When the roving is blocked between the upper entry roll and the blocking device, the fiber tuft created in the forefield extends up to the drawing nip, ergo into the twin belt assembly. The thus relatively long fiber tuft has then a cross section which decreased over this long area. Thus, when restating the machine, a relatively long period of time is required until the fibers emerging from the final pair of exit rolls of the draw frame have again attained a cross section resulting in a full, unobjectional thread.
Furthermore, there exists the danger, with both roving materials that the completely or partially free-standing tuft in the area in front of the drawing rollers will not enter the subsequent nip point on restart, since the movement of the free-standing roving is performed by sliding the roving from its upstream end.
Although it is known (see the previously cited DE-PS No. 3 21 196) to arrange a guide plate below the roving in the forefield area, which has the purpose of preventing the fiber tuft from falling down and to guide it to the following drawing roller pair, positive guidance is not always assured because during the initial movement of the roving its sliding exposed fibers may encounter resistance on the guide plate. When this occurs the fibers may ball themselves up in a compressed manner, lift the roving off the guide plate and deflect it from the desired path. A further possibility for interfering with the proper guidance of forward end of the roving occurs from the travelling blowers used for cleaning the machine. A strong purifying air stream is directed from a blower which travels alongside the machine. This air stream is capable of blowing the exposed fiber tuft and its exposed parts aside, as well as snapping them off the roving, and blowing them from the guide plate. There exists therefore the danger in every case that the roving will not enter the subsequent clamping point of the drawing rollers, causing it possibly to contact rotating parts of the draw mechanism, be caught and pulled up by the latter to form a coil. The use of the guide plate supporting the beginning of the roving is limiting and prevents a shortening of the length of the forefield so that adjustment to a material of different staple length cannot be made unless serial guide plates of different length are provided.
The present invention has the task of eliminating these shortcomings and of creating simple arrangements which assure that a roving is held fast in case of yarn breakage between the upper entry roll and a blocking member, while insuring its free running into the nip point of the draw rollers following the pair of entry rolls. Even if the starting section of the roving has been exposed previously to a purifying airstream sweeping over the draw frame.